LID – Light Induced Degradation

LID – Light Induced Degradation

LID is the degradation of the module arising in the first few hours of exposure to the sun. It particularly affects high efficiency modules. Let’s take a dive into the different aspects of raw materials and production to understand why. 

Nowadays in the production of PV cells there is the tendency toemploy PERC technology (Passive Emitter Rear Cell). This allows the mass production of cells with an efficiency above 20%, with a slight adjustment of the same machinery used for standard cells production.

LID degradation is ascribed to the presence of defective Boron-Oxygen complex in the wafer used to produce the PV cell. This issue affects silicon wafers produced by the Czochralski process, which account for 95% of cells worldwide. LID can be reduced to zero through a “re-cooking” process of the cell: if it is placed at 200 °C for 30 minutes the Boron-Oxygen complex is then separated. However, this re-generation process can vary according to the quality of the wafer used.

It is therefore necessary to use cells and to apply production processes that guarantee the lowest possible LID. If not, there is a risk that that a panel, from the start, produces less power than declared. The loss is normally between 1 and 5%.

High efficiency monocrystalline cells are more affected by this problem, hence the reason why it has become more widespread in the last few years.

FuturaSun® carefully checks its cell suppliers in order to guarantee that the nominal power of the module corresponds to the real power output.

Unfortunately the official tests required by IEC 61215 are not capable of clearly identifying this problem due to the limited exposition of the modules to light –natural or artificial- prior to the checks.